The present disclosure generally relates to a surface size for cellulosic products, and more particularly, to blends of anionic copolymers suitable for surface size.
Paper and other cellulosic products often are sized, i.e., are treated by deposition of a composition to ameliorate characteristics related to the porosity and the hydrophobicity of the cellulosic product. Sizing typically is used to control absorption by the substrate of water, water-borne compositions, and inks. Sizing may be accomplished via an internal sizing process, a surface sizing process, or a combination of both.
In an internal sizing process sizing is initiated before the cellulosic product is completely formed. Internal sizing (also known as bulk sizing), is typically accomplished by adding an internal sizing agent directly to an aqueous pulp slurry such that the internal sizing agent coats the fibers of the pulp. Internal sizing agents are generally hydrophobic in nature, wherein their nonpolar portions are anchored to the surface of fibers and thereby retard water penetration when the fibers are completely formed or fabricated into the finished cellulosic product.
Surface sizing is also referred to as external, tub, or calendar sizing. In a surface sizing process, sizing agents are applied to at least one surface of the finished cellulosic product. More particularly, surface sizing occurs when a surface sizing material is applied to the surface of a fabricated cellulosic product and fills the capillaries of the product, thereby rendering water penetration more difficult. Surface sizing is generally less expensive than internal sizing, because almost the entire sizing agent is retained on the surface of the treated product.
While there are a variety of known sizing systems, a continual need exists for an external sizing system that provides improved sizing performance (e.g., higher Hercules Size Test (HST) values) over known sizing systems.